1. Field of the Invention
The present invention relates to a navigation system that sets an optimum path to connect a start point to a destination by means of a route search.
2. Description of the Related Art
Generally, the car navigation system detects the present position of a car, reads out the map data near the position of the car from the CD-ROM, and illustrates it on the display. On the center of the display screen, a vehicle position marker is presented to indicate the position of the car. The adjoining map data is scrolled around this vehicle position marker as the car travels, so that the map information around the present position of the car can always be obtained.
Usually, the car navigation system contains a route guiding function that enables a driver to travel to a desired destination without taking a wrong path. This route guiding function automatically searches, using a search layer data stored in the CD-ROM, a route of the lowest cost to connect from the start point to the destination by means of a simulated calculation such as the lateral search (BFS) method or the Dijkstra method, and stores the searched route as a guide route. While traveling, the route guiding function displays the map to draw the guide route thick with a different color from those of the other roads. And, when the car approaches an intersection where to change the course on the guide route within a certain distance, the route guiding function presents an enlarged view of the intersection and displays the traveling direction with an arrow, and so forth, thereby guiding the driver to the destination.
The foregoing cost is defined in the dimension of time, and contains a time required for passing through a section and a time required for passing through an intersection, etc. Generally, the route guiding function sets the average speed of a car on the basis of the width of a road and the type of a road (general road, or highway), etc., and obtains a time required for passing through the road, and on this time it adds a time in which the right-turn and left-turn, and the like at the intersection are taken into consideration to thereby obtain the cost.
However, the cost of a road used in searching a route is calculated on the basis of the average vehicle speed estimated in correspondence with the type of a road and the like, and in many cases it does not reflect the real circumstances of the road, which can be a hindrance to obtain a correct route. Suppose two national roads with the same width, for example, one of which passes through an urban area and another one is a by-pass to divert this urban area. In this case, the times required for passing through an identical distance on both the roads are different greatly; and therefore, if the times required for passing through these roads are calculated uniformly, it will not give a correct route.
Recently, the vehicle information communication system (VICS) has been put to practical use, which provides a dynamic information on a traffic jam reflecting the real circumstances of a road. However, the VICS service does not cover the whole country, and outside of the VICS service, the cost calculation based on the average vehicle speed is still carried out, so that a correct route search cannot be achieved.
Further, since the real circumstances of a road is not reflected as described above, the calculation of a required time for the guide route obtained as a result of the route search and an estimated time when to reach the destination will contain a large error, which makes a correct display impossible.
The present invention has been made in view of the foregoing problems, and an object of the present invention is to provide a navigation system that is able to make a correct calculation of the cost while searching or guiding a route.
In order to accomplish the foregoing object, the navigation system of the present invention is provided with search data storage means that stores search data including a statistical required time to represent an actual time required for passing through a road, and route search processing means that searches a route by using the search data so as to connect a start point to a destination when the two are specified. Further, the route search processing means searches a route, when a traffic information from the VICS center is available, by using the search data including a required time to pass through a road obtained on the basis of the traffic information. And, when the traffic information is not available, the route search processing means searches a routeby using the search data including the statistical required time. Thus, according to the invention, the cost during the route search can accurately be calculated by using the search data including the statistical required time, which leads to a route search that reflects an actual road condition.
Further, the foregoing search data contain a by-pass road flag to indicate whether each of the roads is a by-pass road or not. As to a road where the foregoing statistical required time or the traffic information is not available, the route search processing means precedently sets a road that is judged as a by-pass road as a guide route on the basis of the by-pass road flag. If two roads have the same road type and the same road width, the required time to pass through a road greatly differs depending on whether it is a by-pass road or a general road passing through an urban area. To give the priority to a by-pass road will set a guide route that is more accordant to the real condition of a road.
Further, the navigation system of the invention is provided with route guiding means that guide a car to a destination in accordance with the guide route, road data storage means that stores road data containing an actual time required for passing through a road contained in the guide route as the statistical required time, and required time calculation means that calculates an estimated arrival time at the destination or a required time to reach the destination to inform the driver of the calculation result, on the basis of the statistical required time stored in the road data storage means, while guiding a route by the route guide means. Since the estimated arrival time at the destination or the required time to the destination is calculated by using the statistical required time, an accurate display becomes possible, wherein the real road conditions are taken into account.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.